Amino acids synthesized in biological organisms can function as a protein, only when the polypeptide synthesized from amino acids can form the correct steric structure of the protein. Essentially, the correct formation of the steric structure is consistently, rapidly and efficiently done intracellularly. Cells have a factor promoting the formation of the higher-order structure, which is called the molecular chaperone. Some disadvantage for cells may sometimes occur, such as the insufficiency of molecular chaperone formation or protein denaturation due to the formation of an erroneous sequence. It has been elucidated recently that various diseases emerge because the control system for the higher-order structure of proteins does not work properly.
For example, Alzheimer's disease is a neuropathic disease occurring because the component called amyloid has aggregated together intracellularly. Amyloid generally forms a helix steric structure. In the case of the disease, however, the helix steric structure is transformed into a structure called, cross β structure. Thus, amyloid adheres to each other and accumulates intracellularly, triggering brain nerve damages. Furthermore, neuropathic Huntington's disease occurs, because elongated polyglutamic acid, which are attached to the tail part of the protein, huntintin, due to genetic mutation, is involved in the adhesion of the protein to each other, thereby leading to the failure of cellular functions. Furthermore, it is suggested that the functional impairment of HSP (HSC) as one of molecular chaperones is the pathogenesis of Parkinson's disease, cystic fibrosis, and in some cases of spinocerebellar degeneration.
It has been elucidated that a group of apparently different diseases such as these have the common molecular base, namely the failure in the formation of the higher-order structure of a protein as the underlining pathogenesis. No therapeutic method, which is extremely effective for these diseases, has existed yet. Because any component with an unfolding activity on the higher-order structure of a protein without substrate specificity has not yet been found, protein aggregates, which are the direct cause of such diseases, cannot be targeted and unfolded.
On the other hand, a cell should be so flexible that the structure of protein can be unfolded rapidly during dynamic movements, such as cell migration and cell division. Furthermore, once formed, protein aggregates with an erroneous higher-order structure are quickly unfolded, and transferred to a decomposition system. Although it has been recognized so far that such factor is essential, the factor has not yet been identified, because of the difficulty in the purification thereof.
So as to radically cure various diseases due to the failure in the formation of the higher-order structure of a protein, the aggregation of the diseased protein should essentially be untangled, as described above. It is indispensable therefore that “a factor for unfolding the higher-order structure of a protein” be identified, isolated and purified. Additionally, it is expected that such factor can be used as a very useful material for research in cell biology.
The invention of the application has been achieved in such circumstance. It is an object of the invention to provide a new protein polymer showing a great activity for unfolding the higher-order structure of a protein.